The invention concerns a process and equipment for the commercial indirect extrusion of long, essentially straight lengths of metal, in particular long as-cast billets, into sections or the like using a split container which clamps onto the billet when in the closed position and into which a shaping die mounted on a hollow extrusion stem is forced.
A process which is known to be used for the production of sections from billets which are considerably longer than the container involves continuously pushing the billet into the shaping die which closes off the container at one end. The force to overcome the friction in the container and the force for the shaping process itself must be produced by a feeding device and must be transmitted by the part of the billet which is still outside the undivided container. This part of the billet is unsupported at the sides which results in the disadvantage that there is a relatively low upper limit to the extrusion ratio which can be employed. The extrusion ratio can be increased if the material in the container immediately in front of the die is heated. Since this heating, however, depends on the thermal conductivities of the container wall and the billet material, it determines the upper limit of the extrusion rate.
Hydrostatic extrusion is another method known for the commercial extrusion of long billets through a cylindrical container. In this case the cylindrical container is closed off at one end by a shaping die, and a liquid introduced into the container surrounding the billet on all sides before extruding the billet under pressure from all sides. There are however many disadvantages associated with this process, e.g., the temperature of extrusion is limited because of the danger of decomposing the compression fluid, and so for any given extrusion ratio greater extrusion force is required. Furthermore, the storage of elastic energy in the compression fluid and the resultant tendency for the extrusion to emerge in a series of jerks makes it necessary to use seals which can withstand fluids under high pressure; the internal diameter of the container has to be larger in order to accommodate the compression fluid and billets with particularly clean surface have to be chosen.